But as the two companies increasingly compete with each other, the CEOs are now on the outs. Benioff was removed as a keynote speaker from last year's OpenWorld—so he set up a rival keynote across the street. He wasn't even invited to this year's conference.

Salesforce's job ad appeared a few days after Ellison's remarks. It says that project involves the "design and implement major pieces of the Salesforce.com core database infrastructure" using PostgreSQL.

Salesforce.com wouldn't comment on the project, or the rumors that this was an attempt to switch away from Oracle.

"We're always evaluating/exploring different technologies," a Salesforce spokesperson told Business Insider. "We have a broad strategy when it comes to data persistence which includes not only Oracle, but also Postgres, HBase, homegrown file storage, etc."

But some important backers of PostgreSQL sure are excited.

A company called EnterpriseDB makes money by offering commercial support for a version of PostgreSQL.

In the past four years, EnterpriseDB has grown its customer base from about 200 in 2008, to about 2,000 today, including Sony Online Entertainment and TD Ameritrade Ed Boyajian, the company's CEO, Ed Boyajian, told Business Insider. (Skype and Instagram famously use the free, open source version, too.)

"Many of those customers have migrated off Oracle," he said. "That's our primary business."

He added that when a company "of the scale" of Salesforce.com is seen making "making a big commitment" to PostgreSQL, more enterprises will view it as a viable alternative to the Oracle database, too.